Creating a garden pond: how to choose the right lining

Ponds, pools and water features can be great talking points in your garden – and they can be calming to look at, too. Most of us, however, are not blessed with natural streams or rivers running through our plot and must dig a hole and use a liner to create a structure to keep all that water in place. Choosing the right liner, as technical as it might sometimes sound, can make all the difference. Here is a summary of the various ways you can go about it, starting with clay, the traditional method.

Puddling clay

I used clay recently on a project. We were doing some landscaping when we exposed a Second World War bomb. It had to be detonated by the bomb squad – and the next thing we knew, the lake had sprung a leak. Of course, the bomb might not have caused it, but it does make an exciting story.

Still, finding clay to plug the gap was not straightforward. I eventually contacted Sue Sharples, from SJR Contractors Ltd (sjrcontractors.co.uk), which sources landscape materials. The puddling clay she sources comes tested and certified from Peter Callington (puddlingclay.co.uk), who has large reserves on his land.

This clay meets the British Waterways requirements for permeability and costs about £13/sq m, if you lay it the standard 150mm thick. Roll the puddling clay over a hole (like rolling pastry), before wetting it and compacting it with a mini-digger. Finally, cover with about 100mm of soil to stop the clay drying out. Many canals are made this way, with clay forming the characteristic vertical sides. It takes skill to work with clay and transport costs can be high.

Bentomat on a roll

If you like the idea of a natural material with a light carbon footprint, but are daunted by having to employ contractors, Bentomat (bentomat.co.uk) might suit you. Bentomat consists of a 7mm layer of betonite clay (Sodium bentonite) sandwiched between a non-woven fabric top and woven polymer black fabric on the underside. This comes in rolls (the smallest is 5m by 1.1m).

A Gartenart pond creationCredit:
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Its simple installation is a bonus. First, dig out your pool with a maximum gradient of 1:2 on the sides and lay the Bentomat. Overlap the sheets by 15cm. Then cover the mat with 30cm soil. This should be poor subsoil rather than fertile topsoil, to prevent a huge algal bloom from developing in the water due to high phosphate and nitrogen levels (tackling this later can be difficult). You can also buy bags of loose Bentonite (£10 for 25kg).

Jay Rooney, who owns Bentomat, supplies the National Trust and Froglife, among other ventures. One of the main advantages, he points out, is that if this material is punctured it self-seals immediately. It is also thought to last for more than 100 years; and it is easy to install yourself if you’re trying to create a natural-looking pool with soft surrounds. If you want a hard edge to your pool, such as paving, you’ll need to spend a bit of time on the detail, but your project would still be relatively straightforward. Bentomat costs from £3 per sq m for large quantities.

Manmade materials

“Presenters on television often describe the liners they use as 'butyl’,” says Ruth Low, director of Gordon Low (gordonlowproducts.co.uk), the leading manufacturer of pool liners. But she warns that they are often made of another material. Demand from the Far East for the butyl polymer has made it particularly expensive, so nowadays usually manufacturers opt for EPDM (ethylene propylene diene monomer) instead. The term “butyl” has become generic; it used be a mix of 70 per cent butyl polymer and 30 per cent EPDM, but is now usually all EPDM.

PVC and EPDM

The most common type of liners are PVC and EPDM. When these were used for ponds in the Sixties, they dramatically changed the habitat of many domestic gardens, providing an oasis for birds, bees and other wildlife. Low, whose uncle Gordon started the company more than 50 years ago, explained the pros and cons to me. PVC is ideal for smaller ponds, formal or informal. It often comes with a lifetime guarantee, although that excludes root penetration and puncturing (by dogs, badgers or people).

It is available on a roll and in packs (from £2.60 per square metre). With both PVC and EPDM, it’s worth putting down underlay first. I usually put overlay on top, too. Both the underlay and overlay should be 250g per sq m so that the pond structure can hold as much water as possible.

A Gartenart swimming pond might be more adventurous than a conventional pondCredit:
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EPDM facts

There are two main producers of EPDM and it is sold under several tradenames, including SealEco, Firestone and Greenseal.

Greenseal and SealEco is available in 0.75mm thick (from £5.80 per sq m) and 1mm thick versions. Firestone is 1.02mm thick (from £6.20 per sq m) and is supplied by Gartenart (gartenart.co.uk) and Kingcombe Aquacare (kingcombe.com).

You might think that the thicker material is stronger, but extra thickness rarely prevents punctures. The thinner version actually makes flatter, neater folds, so if you are bringing the liner vertically to sit close to paving edges of a pool, this material might suit you better.

EPDM makes a great all-round liner and is very widely used. The thicker version (1.02mm) is robust, and can be used in any situation where tight tucks and folds are unnecessary.

Custom-made liners

More and more people are asking for liners to be made to fit their pools, according to Low. This means that for circular pools, you can avoid the excess folds that you would otherwise get if you used a square sheet. Custom-made liners can cost 50 per cent more and are especially popular for natural swimming pools.

If you get a hole in your custom-made liner, you should be able to repair it quite easily. Just patch it up with tools from a bicycle repair kit. It sounds very Heath Robinson, but these sorts of patches can be easy, effective and long lasting. I’ve done it!

Fibreglass for formality

Finally, I’ve been persuaded recently that fibreglass can be a good option for formal pools. As Nick Roberts, of Fountains Direct, explained, although it is more expensive (at about £50 per sq m), it is easy to clean, you can walk on it and it will never puncture or rip.

Fibreglass is glass-reinforced polyester. It is applied 4-5mm thick onto a solid base, which could be concrete, sheets of ply or similar. It is usually black and can be designed to allow for complicated inlets for water and electrics for fountains and lights.